1. Field of the Invention
The present invention relates to an electronic device and a manufacturing method thereof. Particularly, the invention is useful in inspecting a bonding connection state when a circuit element such as a magnetic sensor built-in chip is connected onto a circuit wiring board by bonding.
2. Description of the Prior Art
As an electronic device, an electronic compass having a magnetic sensor circuit therein will be described hereinbelow. The case where a Pch MOS transistor and an Nch MOS transistor are used as switching devices or switching elements will be explained (the phrases xe2x80x9cswitching elementsxe2x80x9d and xe2x80x9cswitching devicesxe2x80x9d are used interchangeably herein).
FIG. 8 is a schematic diagram of wiring patterns on the surface of a circuit wiring board, on which a conventional magnetic sensor circuit is formed. On the circuit wiring board, in a Pch MOS transistor mounting portion and an Nch MOS transistor mounting portion, wiring patterns Pa1 and Pa2 for connecting lead terminals of the respective MOS transistors are formed.
The wiring pattern Pa1 is a pattern for connecting two terminals, which are connected in parallel with each other, to drain terminals in the respective MOS transistors and for connecting them to +FL terminals of X-axis [sensors] sensor 10 and Y-axis sensor 20. The wiring pattern Pa2 is a pattern for connecting two terminals, which are connected in parallel with each other, to the drain terminals in the respective MOS transistors and for connecting them to xe2x88x92FL terminals of the X-axis sensor 10 and Y-axis sensor 20.
That is, the wiring pattern Pa1 is the wiring pattern for connecting the +FL terminal of the X-axis sensor 10 and the +FL terminal of a Y-axis sensor 20 to the drain terminals formed in the respective MOS transistors. The wiring pattern Pa2 is the wiring pattern for connecting the xe2x88x92FL terminal of the X-axis sensor 10 and the xe2x88x92FL terminal of the Y-axis sensor 20 to the drain terminals formed in the respective MOS transistors. Consequently, the portion between the terminals (+FL) and (xe2x88x92FL) of the X-axis sensor 10 and the portion between the terminals (+FL) and (xe2x88x92FL) of the Y-axis sensor 20 are connected in parallel with each other.
FIG. 9 shows the detail circuit of FIG. 8 and the configuration of a circuit for measuring a flip coil resistance. The X-axis sensor 10 and the Y-axis sensor 20 are magnetic sensors. The sensor 10 comprises a flip coil (FL) 11 and resistors 12, 13, 14, and 15, in which magnetic resistor elements are connected as a Wheatstone bridge. The sensor 20 comprises an FL 21 and resistors 22, 23, 24, and 25, in which magnetic resistor elements are connected as a Wheatstone bridge. An earth terminal 16 is connected between the resistors 14 and 15. An earth terminal 26 is connected between the resistors 24 and 25.
A voltage obtained by detecting a magnetic field in the X-axial direction is outputted from CHxH derived between the resistors 13 and 15 and CHxL derived between the resistors 12 and 14 and is then converted into a digital value by an A/D converter 30 in a subsequent step. On the other hand, a voltage obtained by detecting a magnetic field in the Y-axial direction is outputted from CHyH derived between the resistors 23 and 25 and CHyL derived between the resistors 22 and 24 and is then converted into a digital value by the A/D converter 30 in the subsequent step.
The A/D converter 30 comprises: Nch MOS transistors 31 and 32 as switching elements for operating the X-axis sensor 10 and the Y-axis sensor 20; a constant-current power supply 33 connected to the Nch MOS transistors 31 and 32; and an earth terminal 34 connected to the other terminal of the constant-current power supply 33. The Nch MOS transistor 31 is connected between the resistors 12 and 13 and the Nch MOS transistor 32 is connected between the resistors 22 and 23.
Furthermore, on the circuit wiring board, Nch MOS transistor mounting patterns (hereinbelow, referred to as xe2x80x9cmounting patternsxe2x80x9d) 41, 42, . . . , 48 and Pch MOS transistor mounting patterns (hereinbelow, referred to as xe2x80x9cmounting patternsxe2x80x9d) 51, 51, . . . , 58 are formed. Particularly, the mounting patterns 47 and 48 are connected to the patterns 53 and 54, respectively, and they are connected to the +FL terminals of the X-axis sensor 10 and the Y-axis sensor 20. Namely, it is the wiring pattern Pa1 described in FIG. 8. The mounting patterns 45 and 46 are connected to the patterns 51 and 52, respectively, and they are connected to the xe2x88x92FL terminals of the X-axis sensor 10 and the Y-axis sensor 20. That is, it is the wiring pattern Pa2 explained in FIG. 8. Thus, the flip coil 11 is connected in parallel to the flip coil 12.
The mounting patterns 41 and 43 are connected to an earth terminal 49. A signal N2 is supplied to the mounting pattern 42. A signal N1 is supplied to the mounting pattern 44. The mounting patterns 55 and 57 are connected in parallel to a moiety comprising a capacitor 71 connected to an earth terminal 70 and a direct-current power supply 73 connected to a resistor 72. The direct-current power supply 73 is connected to an earth terminal 74.
A signal P2 is supplied to the mounting pattern 56 and a signal P1 is supplied to the mounting pattern 58. The signals P1 and P2 drive transistors in a Pch MOS transistor 80, which will be described later. The signals N1 and N2 drive transistors in an Nch MOS transistor 90, which will be described later.
In a case where the resistance of each of the flip coils 11 and 12 is measured, since the resistance of each of the flip coils 11 and 12 is as small as several ohms, contact resistances 60 and 62 with connect pins of jigs and wiring resistances 61 and 63 between the connect pins of the jigs and a measuring device cannot be ignored. In consideration of them, the contact resistance 60, wiring resistance 61, contact resistance 62, wiring resistance 63, and constant-current power supply 64 are connected in series. A voltmeter 65 is connected in parallel with the constant-current power supply 64. The contact resistances 60 and 62 are connected to the mounting patterns 46 and 54, respectively. The resistances of the flip coils 11 and 20 are obtained on the basis of measurement by the voltmeter 65. Thus, the bonding connection state is inspected.
FIG. 10 shows a case where MOS transistors are mounted on the circuit constructional diagram shown in FIG. 9. As shown in the diagram, the package of the Pch MOS transistor 80 is SSOT. Lead terminals of the transistor are connected to the mounting patterns 51 to 58 by soldering, so that the transistor is mounted on the circuit wiring board. Lead terminals of the Nch MOS transistor 90 are connected to the mounting patterns 41 to 48 by soldering, so that the transistor is mounted on the circuit wiring board.
Lead terminals 81 and 82 of the Pch MOS transistor 80 are connected in parallel to a drain terminal of a switching element 80a. Terminals 83 and 84 of the Pch MOS transistor 80 are connected in parallel to a drain terminal of a switching element 80b. Terminal 91 and 92 of the Nch MOS transistor 90 are connected in parallel to a drain terminal of a switching element 90a. Terminals 93 and 94 of the Nch MOS transistor 90 are connected in parallel to a drain terminal of the switching element 90b. 
The operation of the magnetic sensor circuit with the above-mentioned configuration will now be described. FIG. 11 is an explanatory diagram of the operation of the magnetic sensor circuit. FIG. 11A is a timing chart. FIG. 11B is a V-B graph. First, a control unit (not shown) sets the signal P1 to a low level L and sets the signal N2 to a high level H to operate the flip coils 11 and 12, thereby generating flip magnetic fields. Subsequently, the control unit (not shown) makes the MOS transistor 31 conductive with a gate signal R1 and allows the X-axis sensor 10 to detect the magnetic field (earth""s magnetic field), thereby outputting a voltage Vxs from CHxHxe2x88x92CHxL. The control unit also makes the MOS transistor 32 conductive with a gate signal R2 and allows the Y-axis sensor 20 to detect the magnetic field (earth""s magnetic field), thereby outputting a voltage Vys from CHyHxe2x88x92CHyL.
Subsequently, the control unit (not shown) sets the signal P2 to a low level L and sets the signal N1 to a high level H to operate the flip coils 11 and 12, thereby generating flip magnetic fields opposite to the preceding flip magnetic fields. The control unit (not shown) makes the MOS transistor 31 conductive with the gate signal R1 and allows the X-axis sensor 10 to detect the magnetic field (earth""s magnetic field), thereby generating a voltage Vxr from CHxHxe2x88x92CHxL. The control unit also makes the MOS transistor 32 conductive with the gate signal R2 and allows the Y-axis sensor 20 to detect the magnetic field (earth""s magnetic field), thereby outputting a voltage Vyr from ChyHxe2x88x92CHyL.
On the other hand, as for Vs (Vxs, Vys) and Vr (Vxr, Vyr) outputted as mentioned above, as shown in FIG. 11B, the magnetic resistor elements are magnetized in a predetermined direction or a direction opposite thereto by the flip magnetic fields of the flip coils 11 and 12, so that lines Vs and Vr having different inclinations negative and positive to a magnetic field (earth""s magnetic field) B[uT] are drawn. Vsxe2x88x92Vr is set to a detected voltage of the magnetic field and Vsxe2x88x92Vr of a zero magnetic field is shown as an offset voltage Vofst. The control unit (not shown) executes the calculation. The above-mentioned magnetic sensors such as X-axis sensor 10 and Y-axis sensor 20 for detecting a change in magnetic field for one axis are disclosed in PCT/EP 94/01789 (U.S. Pat. No. 5,521,501, Japanese PCT Patent Application Laid-Open No. 8-503778).
The above-mentioned magnetic sensor circuit is the magnetic sensor for detecting a magnetic field for one axis. Accordingly, when it is used for an electronic compass for detecting directions by two axes, magnetic sensors are needed as much as the directions. It is necessary in the magnetic sensors with the flip coils that the directions of the flip magnetic fields of the flip coils are made to coincide with each other to synchronize two axes, thereby outputting a voltage. Accordingly, as mentioned above, it is necessary that the flip coils be connected in parallel to a driving circuit and both the flip coils are simultaneously driven.
However, in the conventional case, the wiring patterns are connected in parallel to each other, thereby connecting the flip coils in parallel to each other. Accordingly, when the magnetic sensor built-in chip is mounted on the circuit wiring board and is connected to the board by bonding and the bonding connection state is then detected, the state cannot be determined in some cases.
For example, the quality of the bonding connection of the flip coils of the above-mentioned magnetic sensors connected on the circuit board by bonding is generally determined by measuring the resistances of the flip coils connected in parallel to each other. In a case where the bonding connection of the two flip coils is precisely made, resulting in no disconnection, the total resistance is several ohms. In the case where the bonding operations for both the coils are failed, resulting in failures, the total resistance is several megohms. Accordingly, since the orders of both the cases are different from each other, the failure can be easily found.
However, when one of the bonding operations for the two flip coils is disconnected, a difference between the resistance thereof and that in the case of the good quality is about 1xcexa9. In consideration of a measurement error or the like, it is difficult to discriminate disconnection from good connection and the failure cannot be easily found. Particularly, to obtain measurement precision of several ohms through an inspecting device for mass production, in consideration of a wiring resistance between a jig and a measuring device, a determined value should be finely adjusted. Accordingly, it results in a barrier on improvement of efficiencies of inspecting time and the like.
Accordingly, the present invention is made in consideration of the above problems and it is an object of the invention to provide an electronic device which can easily determine the failure in bonding connection precisely even with low measurement precision as in the case of an inspecting device for mass production, and a manufacturing method thereof.
To accomplish the above object, according to the present invention, an electronic device comprises: a first magnetic sensor including a first flip coil having a first terminal and a second terminal; a second magnetic sensor including a second flip coil having a third terminal and a fourth terminal; and a driving circuit for driving the first and second sensors, wherein the first terminal is connected to the third terminal on a circuit wiring board, and the second terminal is connected to the fourth terminal by mounting the driving circuit on the circuit wiring board.
In the above configuration, preferably, the electronic device according to the invention further comprises a plurality of switching elements in which a plurality of output terminals are connected on the inside, wherein a first output terminal of a first switching element is connected to a first output terminal of a third switching element, a second output terminal of the first switching element is connected to a second output terminal of the third switching element, first and second output terminals of a second switching element are connected to first and second output terminals of a fourth switching element, the first output terminal of the first switching element is connected to the fourth terminal of the second flip coil, the second output terminal of the first switching element is connected to the second terminal of the first flip coil, and the first and second output terminals of the second switching element are connected to the first terminal of the first flip coil and the third terminal of the second flip coil, respectively.
In the above configuration, preferably, the electronic device according to the invention further comprises a plurality of switching elements, wherein an output terminal of a first switching element, an output terminal of a third switching element, the fourth terminal of the second flip coil, and the second terminal of the first flip coil are connected, and an output terminal of a second switching element, an output terminal of a fourth switching element, the first terminal of the first flip coil, and the third terminal of the second flip coil are connected.
A manufacturing method of the electronic device according to the invention, comprises the steps of: mounting a first magnetic sensor including a first flip coil having first and second terminals on a circuit wiring board; mounting a second magnetic sensor including a second flip coil having third and fourth terminals on the circuit wiring board so that the first terminal is connected to the third terminal; measuring a first resistance between the first terminal and the second terminal; measuring a second resistance between the first terminal and the third terminal; and when at least one of the first resistance and the second resistance exceeds a predetermined resistance, determining that a disconnection failure occurs.
Accordingly, there is provided a magnetic sensor circuit constructed in such a manner that at least one magnetic sensor built-in chip, which has therein at least two magnetic sensors each for detecting a magnetic field (earth""s magnetic field) in one axial direction and flip coils each for generating a pulse magnetic field fluctuating every magnetic sensor, is mounted on wiring patterns of the circuit wiring board by bonding, and a driving circuit having a pair of MOS transistors for generating different voltages positive and negative to be outputted to the flip coils is connected in parallel to at least the two flip coils. In a case where a bonding connection state of the magnetic sensor built-in chip to connect the terminal of the flip coils to the wiring patterns is inspected, before the MOS transistors are mounted on the circuit wiring board, on which the wiring patterns for serially connecting the terminals connected in parallel with each other in the MOS transistors to the terminals of each magnetic sensor built-in chip are formed, the magnetic sensor built-in chip is mounted on the board and the terminals are connected to the wiring patterns by bonding and terminals for inspection of an inspecting device are then come into contact with the wiring patterns and are electrically connected to each other to measure the resistances of the two flip coils, respectively, so that the connection state of the magnetic sensor built-in chip can be inspected on the basis of the resistances. The inspection can be performed on the basis of current values, voltage values, resistances, or a combination of at least two values of them.
Consequently, according to the invention, in a case where circuit elements such as magnetic sensors (flip coils), namely, X-axis sensor and Y-axis sensor are connected onto the circuit wiring board by bonding before the MOS transistors are mounted on the board, when the bonding connection is correctly made, the circuit elements such as flip coils are serially connected to the wiring patterns. In such a state, therefore, a resistance indicates the sum of the resistances of the circuit elements such as flip coils. When one of the circuit elements, namely, one flip coil is broken, the resistance is remarkably different from that in the case where the bonding is correctly made. Particularly, when the bonding connection of the magnetic sensor built-in chip is disconnected, a resistance in an unconnected case is indicated. Accordingly, the resistance in the unconnected case is previously recognized and the present resistance is compared with that in the unconnected case, so that the disconnection can be determined.
According to the invention, therefore, since the determination can be made by a comparable measured value even with low measurement precision as in the case of an inspecting device for mass production, a bonding connection failure of the circuit element such as a magnetic sensor circuit can be precisely determined easily. As a measured value such as a resistance before mounting the MOS transistors, a value supposed by design is used as a comparison determination value. Upon inspection, a measured value such as a resistance before mounting may be measured every product.